The use of a stylus with a touch screen interface is well established. Touch screen designs have incorporated many different technologies including resistive, capacitive, inductive, and radio frequency sensing arrays. Resistive touch screens, for example, are passive devices well suited for use with a passive stylus.
Various active stylus devices have been implemented for use with touch screens and are found in many consumer applications such as point-of-sale terminals (e.g., the signature pad used for credit card transactions in retail stores) and other public uses.
Active stylus devices can fall broadly into two categories: inductive and electrostatic. In inductive stylus devices, an AC signal is generated and is fed to the tip of the stylus, and sensors behind or around the touch screen receive the signal. The relative magnitude of the received signal at each of the sensors is used to interpolate the position of the stylus tip. In electrostatic stylus devices, an electrostatic field is generated at the tip of the stylus and is detected by a self-capacitance touchscreen.